so we've extend our one way lighting circuit now to be a two way lighting circuit in other
words the two switches behind me control the one lighting points we've got two-way control
of our lighting point we're going to carry out the continuity of CPC and polarity test followed
by the insulation resistance as we did with our one-way light in circuit we have the link in the
consumers unit ready for our continuity test I've also set my MFT up to measure ohms because we're
measuring resistance during the continuity test and we're going to carry out the continuity of CPC
first and then we're going to include the priority test at the same time once that's completed and
covers will be on or low to be removed and we'll go on to the insulation resistance
test so I've set an instrument as I suggested in my continuity of CPC and polarity of my one-way
lighting circuits I've removed the resistance of the leads on the tester and I've confirmed
and removed the resistance of the link the link is in place and we're going to measure every point on
our radial circuit for continuity of CPC and we're gonna prove polarity at every lighting
point we have only one lighting point but this time we have two switches that need continuity
proving at them during the polarity test we will operate first second first second switch is seeing
full scale deflection of our instrument proving that the circuit will go open and closed or on
and off at the lighting point leaving it in the on position for the insulation resistance test that
comes later on logic suggests to us that this is the furthest point on our radial circuit however
it is in it's still the lighting point if we think and follow through the path of the line conductor
we take the line conductor from the consumers unit and it comes into the center loop termination from
the center loop termination we bring it down to the switch from the switch it goes through the
three core to the other switch and then obviously from the other switch background to the switching
line that turns on the lamp itself so even though it looks as if the light input is closer to the
consumer unit the amount of cable through the switching so in other words down through the
common and rappers and background again means the lighting point is the furthest point on
this radial circuit and we should achieve our highest reading at this point however we will
record the highest reading wherever we achieve it whether it be one of the switches or at the
lighting point but logic says the maximum amount of cable on the switching line conductor and CPC
is actually at the lighting point so first of all we do the lighting point I'm going to connect on
to the earthing terminal within the lighting point where the CPC's are connected and the switching
line conductor so we can prove polarity at the same time the instrument itself has been zeroed
and hopefully we get a realistic reading as we do the test so the minute I've got 0.38 of an ohms
and the circuit is recording a reading therefore we're in the on position in other words the switch
is closed let's prove polarity at the same time so our instrument now has gone to an infinite
reading or open circuit full scale deflection from a reading to no reading we go to the second
switch our circuit has come back on we've got a slightly different reading now of 0.2 of an
ohm the switches at college hardly get used so as we open and close the switch blades we can see a
slight variation in the resistance so back to the first switch and we should see it go off and we
have and then we'll go back again to the second switch and we have got a settled down reading
of zero point two one ohms at the moment that's our highest reading is the only one we've taken
we need to remember that reading because we're now going to do a continuity test at each of the
switches and record the highest reading wherever we achieve it we will leave the switches in the on
position because the insulation resistance test that comes later on requires all switches to be
left on so next we need to prove continuity of the CPC at the switch itself probably on to the Earth
terminal in the back and one of the terminals within the two-way switch I get a reading of
0.1 9 of an ohm I don't need to operate the switch of this stage the switch needs to be operated when
you're proving polarity of the lighting point itself and not when you're proving continuity
of the CPC at the switch move over to the second switch again the probe on to the earthing terminal
and one of the terminals within the actual switch itself I've got zero point two two of an ohm of
all the Rings I'll get or record the highest one logic says that should be at the lighting
point itself however we do record the highest one wherever we get it in circuit we can record that
reading now for continuity of CPC under our box heading r1 + r2 r1 representing the continuity of
the line conductor r2 representing the continuity of the CPC we can also now tick the box for
polarity we've proved that both these switches turn on and off the lighting points above we've
left in the on position we need to put the covers back on so we can start the insulation resistance
test next so all the covers have gone on all the loads have been removed in this case there's no
lamp in circuit I've also turned off as before the circuit breaker and the RCC be because the
RCC B contains electronic components and we do not want to pass 5 and D volts DC through that
we've also got the earthing conductor in the tail is connected to the supply Authority's incoming
earth however we have an isolated board so the supply is not live into the distribution board
or consumers unit itself and we're now ready to carry out the insulation resistance test so main
strands been set up as I did and showed you in the insulation resistance test of our one-way lighting
circuit so I've set it into the mega ohm scale and at 500 volts for a single-phase installation
and it doesn't matter which sequence in which we do this test so I'm going to clip on first of all
to the earth bar and I'm then going to go on to the top of the circuit breaker itself trying to
keep my hands out the way and if I press the test button now our reading is greater than the Machine
can read so we've got a reading greater than 9 9 9 mega ohms takeoff and probe on now to my
neutral bar so between the earth and neutral bar I've got a reading greater than 9 9 9 mega ohms
and finally I'm going to test between the neutral bar and the top of the circuit breaker itself and
again press and test the button and I've got a reading greater than 9 9 9 mega ohms however for
this installation that is not the test completed in this installation we have 2-way switching so
there's a slight spin on the test itself so we've completed the insulation resistance test exactly
the same as we did when we did a one-way light in circuit however it is not complete at this stage
we need to walk into the installation and to the to waste which is wherever they are throughout the
installation we've got a set on one set of two waste which is in this case so what we have to
do is throw them into the opposite on position think of it at the moment the line conductor
comes up to the loop terminal comes down to the switch and it comes through say the brown strap
up through black common background and say turns on the light it means the grace trapper hasn't
been tested for insulation resistance we've only tested the black and the brown within the three
core to test the grace wrapper we need to throw it into the opposite on position that goes off
that goes on the circuit line now comes up into the loop terminal down on our twin Brown now
down the grace trapper through around the black common and turns on our life in so we repeat the
insulation resistance s that the distribution board or consumers unit again for the second
time so you walk around the installation thrown all the two-way switches into the opposite on
position return to the dis board and repeat the insulation resistance test so let's repeat the
insulation resistance test so I've walked around my installation and I've thrown the two way
switches into the opposite on position have now returned to the distribution board or consumers
unit and I'm going to repeat the insulation resistance test again for that circuit so
onto the earth bar onto the line bar and press the test button we've got a reading greater than nine
nine nine mega ohms I go into the neutral but I'll repeat the test again I've got a reading greater
than nine nine nine mega ohms I move my crocodile clip on to my neutral bar and I repeat the test
for the final time between line and neutral and I've got a reading greater than ninety nine nine
mega ohms now I've completed the insulation resistance test on this lighting circuit
because I've done it with the two-way switches in both on positions therefore the insulation
resistance has got both strap as that are in circuit tested so if we've only done it once
you'd have only tested the insulation resistance of one strapper by throwing both two-way switches
back into the on position we've complete the insulation resistance because the other strapper
was in circuit on this second insulation resistance test hope this has been some help